The present state of the art of sandblast nozzle is substantially as shown and taught by U.S. Pat. No. 4,269,359, owned by the applicant herein. In such sandblast nozzles, a hose is provided for carrying sand or other abrasive granular material under pressure from a source of such material at one end to the valve mechanism at the other. This valve mechanism presently comprises a tubular metal handle receiving the hose in one end thereof and having a ceramic nozzle at the opposite end. A lever is pivotally mounted to the handle, such lever having one end positioned for engagement by the operator's hand, and the opposite end being provided with an appropriate sealing member for selective engagement with the nozzle orifice.
The sealing member of presently known sandblast valves has typically included a "stop block" or "seal block" of rubber or other resilient material to be brought into contacting engagement with the end of the nozzle and to close the nozzle orifice. Such closure is achieved by simple release of the lever arm, with a spring biasing the lever arm into the closed position. The operator's hand, operating upon the lever and against the bias of the spring, achieves the opening of the valve.
In the prior art, it has been most desirable that the seal blocks of the valve members be of a resilient material such as rubber or the like in order to prevent chipping of the ceramic nozzle when the lever arm is released and the stop block forcefully engages the nozzle tip. However, abrasive material such as employed in sandblasters rapidly destroys the resilient seal block. The time required for such destruction is generally a function of the quickness of the closing action. Operators who slowly close the valve by regulated release of hand pressure on the lever arm more quickly wear out the sealing block than those operators who instantaneously release the lever arm, allowing the spring to attain immediate closure. In any event, it has been found in the prior art that an average operator of such sandblast nozzles would wear out the surface of a seal block after fifty openings/closings of the nozzle. As a result of such wear, the prior art has sought to employ cylindrical or rectangular seal blocks which may be rotated to progressively expose virgin surfaces to the nozzle tip when the prior surface has been worn by the sand. Such seal blocks have typically been mounted axially on a bolt so that they can be rotated to expose the new sealing face when the face wears. However, even utilizing such seal blocks, it has been found that only two hundred openings and closings of the nozzle can typically be achieved without having to totally change the seal block. Of course, it is understood that after each fifty openings and closings the seal block would necessarily be rotated to expose a new face.
Additionally, the prior art has taught the implementation of a deadman valve in the sandblast industry. The state of the art sandblast valve as taught in U.S. Pat. No. 4,269,359 is of such a nature. When the valve is released from the operator's hand, the lever arm automatically closes the valve to prevent sand from being emitted from the nozzle. However, the need of the operator to continually depress the lever gives rise to operator fatigue, since the lever must be constantly urged against the biasing spring. When it is required that the sandblast valve be opened for extended periods of time, there is a need to override the deadman feature. It has been found that most large valves are of sufficient weight that an overriding of the deadman feature does not pose a serious safety problem, since the large valve will not whip around at the end of the hose as by backlash or the like when they are dropped during operation with the valve open. Only the lighter valves have been known to demonstrate such undesirable characteristics and, in those valves, an overriding of the deadman feature is not desirable.